A technology called thin provisioning for dynamically allocating a virtual volume page from a pool, which is a collection of storage areas (pages), in accordance with a request from a host computer is known. This pool is a collection of one or more logical volumes. One page is one storage area obtained by partitioning the logical volume comprising the pool into an arbitrary size. In thin provisioning technology, pool storage areas can be used effectively because an in-pool storage area is allocated only with respect to the portion accessed by the host computer. In a first prior art, multiple types of storage areas (pages) featuring different performance are mixed together in the pool, and a page is sorted by tier based on a performance or other such prescribed criteria. In the first prior art, an appropriate tier is selected in accordance with the characteristics of a virtual volume, and a page belonging to the selected tier is allocated to the virtual volume (Patent Literature 1). This makes it possible in the first prior art to make proper use of a high-performance, high-cost storage area and a low-performance, low-cost storage area, enabling the realization of a virtual volume that reconciles performance and cost.
In addition, as a second prior art, a technology for making it appear as though a logical volume of a second storage control apparatus, which exists outside of a first storage control apparatus, has been incorporated in the first storage control apparatus and is the same as a logical volume unique to the first storage control apparatus is known (Patent Literature 2).